Article

Impacts of extreme ocean warming on the early development of a marine top predator: The Guadalupe fur seal

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Abstract

From fall 2013 through 2015, a large-scale, multi-year warm water anomaly occurred in the northeast Pacific Ocean. The phenomenon had negative impacts on some oceanic predators, including higher mortalities and poor body conditions. We studied the effect of this warm water anomaly on the weight gain of Guadalupe fur seal(Arctocephalus philippii townsendi) neonates off the coast of the Baja California Peninsula, Mexico. Individuals were captured, marked, and weighed every 13–15 days, up to 60 days of age, during the early nursing seasons (mid-June to mid-August) of 2014–2016 at this subspecies’ only reproductive colony, located on Guadalupe Island. The body weight was measured at each capture and recapture. A hierarchical Bayesian model was used to explore the impact of sea surface temperature (SST) anomalies on the neonates’ weights. The hierarchical structure included connected models for the spring-summer SST trend around the colony, the neonatal body weight gain with age, and the relationship between the anomalies of both variables. Marked neonates were also tracked in order to estimate survival rates during first two months of age. Overall, positive SST anomalies had a negative effect on neonatal body weight gain. The northeast Pacific Marine Heatwave precipitated the lowest weights at birth and the slowest weight gain in 2014, as well as low weights and the lowest survival rate in 2015, likely due to the persistence of the warm anomalies. The evident sensitivity of Guadalupe fur seal neonates to regional warming conditions highlights their vulnerability under scenarios of climate change, which could impede this subspecies’ continued recovery from near extinction.

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Applied Hierarchical Modeling in Ecology: Distribution, Abundance, Species Richness offers a new synthesis of the state-of-the-art of hierarchical models for plant and animal distribution, abundance, and community characteristics such as species richness using data collected in metapopulation designs. These types of data are extremely widespread in ecology and its applications in such areas as biodiversity monitoring and fisheries and wildlife management. This first volume explains static models/procedures in the context of hierarchical models that collectively represent a unified approach to ecological research, taking the reader from design, through data collection, and into analyses using a very powerful class of models. Applied Hierarchical Modeling in Ecology, Volume 1 serves as an indispensable manual for practicing field biologists, and as a graduate-level text for students in ecology, conservation biology, fisheries/wildlife management, and related fields. Provides a synthesis of important classes of models about distribution, abundance, and species richness while accommodating imperfect detection Presents models and methods for identifying unmarked individuals and species Written in a step-by-step approach accessible to non-statisticians and provides fully worked examples that serve as a template for readers' analyses Includes companion website containing data sets, code, solutions to exercises, and further information
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Scat analysis and stable isotope analysis (δ13C and δ15N) were used to perform a trophic comparison between two existing Guadalupe fur seal (Arctocephalus philippii townsendi) colonies on Guadalupe Island (GI) and the San Benito Archipelago (SBA) during the 2013 breeding season. The stable isotope analysis included 67 samples from GI and 36 from the SBA, indicating that this otariid is a teuthophagous specialist. The two colonies showed different trophic levels: (1) 4.5 for GI, for which the most dominant prey was the jumbo squid, and (2) 4.0 for the SBA, for which the main item was the opalescent squid. The stable isotope analysis included 15 fur samples from each site. Both analyses were complementary, identifying prey species from an oceanic habitat, with fur seal δ13C values that are typically associated to that environment. Although assigned a higher trophic level (scat analysis), GI had lower δ15N and δ13C values, suggesting latitudinal segregation. These differences between colonies may be related to their distinct age proportions or a strategy to avoid intrapopulation competition. Our contribution regarding trophic variation is based on a snapshot regarding scat analysis and a time window of ~16 wks prior to collection reflected by stable isotope analysis in fur. Additionally, this species is currently experiencing population growth, which increases the possibility of overlap for resources between both colonies. Therefore, it is important to establish baselines and continue these comparative analyses over time to determine their significance within its recovery.
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The steady upward trend in the use of model selection and Bayesian methods in ecological research has made it clear that both approaches to inference are important for modern analysis of models and data. However, in teaching Bayesian methods and in working with our research colleagues, we have noticed a general dissatisfaction with the available literature on Bayesian model selection and multimodel inference. Students and researchers new to Bayesian methods quickly find that the published advice on model selection is often preferential in its treatment of options for analysis, frequently advocating one particular method above others. The recent appearance of many articles and textbooks on Bayesian modeling has provided welcome background on relevant approaches to model selection in the Bayesian framework, but most of these are either very narrowly focused in scope or inaccessible to ecologists. Moreover, the methodological details of Bayesian model selection approaches are spread thinly throughout the literature, appearing in journals from many different fields. Our aim with this guide is to condense the large body of literature on Bayesian approaches to model selection and multimodel inference and present it specifically for quantitative ecologists as neutrally as possible. We also bring to light a few important and fundamental concepts relating directly to model selection that seem to have gone unnoticed in the ecological literature. Throughout, we provide only a minimal discussion of philosophy, preferring instead to examine the breadth of approaches as well as their practical advantages and disadvantages. This guide serves as a reference for ecologists using Bayesian methods, so that they can better understand their options and can make an informed choice that is best aligned with their goals for inference.
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Since 1990, the NOAA National Environmental Satellite Data and Information Service (NESDIS) has provided satellite-derived sea surface temperature (SST) measurements based on nonlinear SST algorithms, using advanced very high resolution radiometer (AVHRR) multiple-infrared window channel data. This paper develops linear and nonlinear SST algorithms from the radiative transfer equation. It is shown that the nonlinear algorithms are more accurate than linear algorithms but that the functional dependence of the nonlinearity is data dependent. This theoretical discussion (sections 2-4) is followed with a discussion in section 5 of the accuracy over a 9-year period of the satellite-derived SST measurements provided by NOAA NESDIS when compared with coincident drifting buoys. Between 1989 and 1998 the global scatter of the daytime satellite SST against drifting buoy measurements has decreased from -0.8 ø to 0.5øC, while the nighttime scatter has remained fairly constant at 0.5øC. An exception to these accuracy measurements occurred after the eruption of Mount Pinatubo in June 1991.
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California sea lion (Zulophus calijoyniunus) scat and spewing samples collected at three rookeries in south- ern California during 1981-95 were used to determine how sea lions utilized the market squid (Lol&o opalescens) resource. The samples revealed that market squid is one of the most important prey of sea lions in southern California, occurring in 35% to 44% of scat samples from San Nicolas Island (SNI), San Clemente Island (SCI), and Santa Barbara Island (SBI). It is eaten by sea lions throughout the year, but most often during fall and win- ter, and patterns suggest periods of high and low con- sumption associated with prevailing oceanographic conditions and, possibly, with squid abundance and movements. Percent frequency of occurrence values for market squid in scat samples collected seasonally from SNI were positively correlated with those from SCI (Y = 0.78), and samples collected during summer at SBI were positively correlated with summer samples from SCI (Y = 0.82) and SNI (Y = 0.85). Landings of market squid at ports in southern California and percent oc- currence values of market squid in scat samples collected seasonally were positively correlated for SNI (Y = 0.66) and SCI (Y = 0.74), but not for summer samples from SBI (Y = 0.25). Sea lions eat squid with dorsal mantle lengths from 10 to 235 mm (mean = 127 mm). Signif- icant seasonal, annual, and interisland differences (P < 0.001) were found in the size of squid consumed by sea lions. Significant differences (P < 0.001) were found in size of squid between scats and spewing, and between individual samples.
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We studied the influence of sex of pup, maternal age, birth date of pup, number of foraging trips, and the mean duration of foraging trips at sea and nursing visits ashore on the growth and mass at weaning of pups of Antarctic fur seals (Arctocephalus gazella) during austral summers of 1988-1990. Although growth and mass at weaning were highly correlated, they were not related to maternal characteristics in 1988 or 1989. However, in 1990 there was a negative relationship between growth of pups and mean duration of foraging trips. Growth rates of males and females varied considerably between 1972 and 1991 and appeared to decline from 1984 through 1990. Methods used to collect and weigh the pups influenced the nature and magnitude of sex differences in estimated growth rates. Growth rates of male and female pups did not differ when weighed serially (same individuals weighed throughout lactation), but males grew faster than females when weighed cross-sectionally (different individuals weighed throughout lactation). Based on our results of pairs of mothers and pups followed over the lactation period, maternal investment was greater in males than females because males were heavier at birth and older at weaning than females and not because of any differential growth between the sexes. Mothers appear to have to work longer, but not harder, to wean males than females. Under the favorable feeding conditions that usually exist, individual differences in the growth of pups are most likely influenced by variation in foraging efficiency of mothers.
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In order to compensate for the resource demands of reproduction, organisms usually increase the amount of total food resources available. This may be achieved by different tactics of resource use that also include foraging decisions. Two such general tactics are discussed in this paper under the concepts of capital and income breeding. These are defined mainly from the temporal distribution of resource acquisition relative to resource use. A capital breeder acquires its resources in advance and store them endogenously or exogenously until they are needed to supply aspects of offspring production. An income breeder, on the other hand, adjusts its food intake concurrently with breeding, without reliance on stores. In a perfectly predictable environment without limited resources, income breeding is the best option since capital breeders may have to pay a number of energetic and demographic costs for their stored resources. However, under unpredictable food conditions, food/time limitations, and risky fora
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1. The reproductive performance of female Antarctic fur seals was examined in relation to age, reproductive experience and environmental variation over 10 consecutive years (1983-92) at Bird Island, South Georgia. 2. The age at which females first gave birth varied from 3 to 6 years; over 90% of these females were 3 or 4 years of age. We found no evidence to suggest that age at primiparity had significant effects on subsequent reproduction; however, 3-year-old primiparae were less likely to be seen in subsequent years than 4-year-old primparae which may indicate a cost, in terms of survival, for females that first give birth at an early age. 3. Age-specific reproductive rates increased rapidly from ages 2 to 6 years, reached a peak of 0.80 at 7-9 years, remained above 0.75 until 11 years and then began to decline with increasing age. 4. The mean duration of foraging trips in the current year (which was used as a measure of the availability of food resources) consistently improved models of the likelihood of pupping and of weaning success. When these trips were long (indicating reduced local food resources), females returned to the breeding beaches later, fewer females pupped, they gave birth to lighter pups and weaning success was reduced. 5. The reproductive performance of older, experienced Antarctic fur seals was greater than that of younger, inexperienced animals because they had higher natality rates, gave birth to heavier pups earlier in the season, had greater weaning success and were more likely to pup the next season.
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A major hypothesis of life history theory is that early development conditions affect future survival and reproductive success. However, although a growing number of studies have addressed this question, many of them are taxonomically biased, thereby impeding the generalization of this hypothesis. This study examines the factors influencing post‐weaning survival in five weaned cohorts of subantarctic fur seal pups from Amsterdam Island, southern Indian Ocean. It used mark–recapture data from 7 consecutive years of different environmental conditions. The cohort return rate varied from 45% to 74% of weaned pups, depending on the year of weaning. In each cohort, 96% of weaned pups returned between 3 and 6 years of age, and none of the factors examined seemed to influence this timing pattern. The probability of survival to this first return was negatively related to sea‐surface temperature anomalies (SSTa) of the 6 months following the weaning process. It increased with pup preweaning growth rate and differed between the sexes. Females’ survival rate was significantly higher than males’, except during years of extreme SSTa, where no difference was detected. The juvenile state represented young individuals after their first return on their native island. Annual juvenile tag loss rate was constant at 0·217 (SE = 0·027), whereas temporary emigration rate varied over cohorts and was higher in males 0·423 (SE = 0·035) than in females 0·170 (SE = 0·012). This dispersion pattern may be prolonged in some cases, as the yearly immigration probability was constant at 0·290 (SE = 0·065). Taking into account tag loss and temporary emigration, the estimated yearly survival probability of juveniles was 0·964 (SE = 0·022). This value was unrelated to any tested oceanographic or individual parameter including sex. Results support the hypothesis that early development traits affect short‐term post‐weaning survival. However, no long‐term effect of maternal postnatal investment was detected after the first return to the native island. Results also indicate that the effect of early development traits on survival interacts with environmental conditions encountered shortly after independence of individuals.
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In order to estimate the effect of weaning mass and body condition on the post‐weaning survival of grey seal pups from the Isle of May, Scotland in 1998 during their first year of life, a simultaneous analysis of live resighting and dead recovery mark–recapture data was used. A new type of tag was employed which allowed individuals to be identified when resighted alive ( Hall, Moss & McConnell 2000 ) as well as when found dead. The probability of post‐weaning survival to age 1 increased with body condition at weaning and differed between the sexes. Regardless of pup condition and time of year, the odds of survival for female pups over a 2‐month interval was estimated to be 3·37 (SE = 1·30) times higher than for males. Regardless of sex, a 1 standard deviation increase in pup condition was estimated to increase the odds of survival by a factor of 1·422 (SE = 0·226). For a male pup in average condition (0·41 kg cm ⁻¹ ) the estimated annual survival after adjusting for tag‐loss was 0·193 (SE = 0·084); for a female pup in average condition (0·39 kg cm ⁻¹ ) it was 0·617 (SE = 0·155). The effect of condition at weaning on survival was significantly greater for male pups than for females. This implies that high quality females should invest more heavily in their male pups because the marginal return, in terms of increased reproductive value, from any additional expenditure is twice that for females. Male pups in our sample were significantly heavier at weaning and in better condition than female pups. However, this does not provide conclusive support for our predictions, because we could not control for the effects of maternal size on weaned mass.